Iron-platinum (FePt) is a most promising candidate for heat-assisted-magnetic-recording (HAMR) applications. Examples of conventional iron-platinum (FePt) medium layer structures are shown in FIGS. 1A to 1C.
FIG. 1A shows a recording medium 100 including a glass substrate 102, a seedlayer 104, a chromium-ruthenium (CrRu) layer 106, a layer 108 of magnesium oxide (MgO), platinum (Pt), titanium carbide (TiC) or titanium nitride (TiN), and a recording layer 110. The seedlayer 104 helps to promote the deposition of a chromium-ruthenium (CrRu) layer 106. The CrRu layer 106 in turn acts as a seedlayer for the growth of the layer 108.
FIG. 1B shows a recording medium 120 including a glass substrate 122, a seedlayer 124, a magnesium oxide (MgO) layer 128, and a recording layer 130. The seedlayer 124 helps to promote the deposition of the magnesium oxide (MgO) layer 128.
FIG. 1C shows a recording medium 140 including a glass substrate 142, a seedlayer 143, a heat sink layer 145, another seedlayer 144, a layer 148 of magnesium oxide (MgO) or platinum (Pt), and a recording layer 150. The seedlayer 143 helps to promote the deposition of the heat sink layer 128 while the seedlayer 144 helps to promote the deposition of the layer 148.
Currently, there are lots of technical challenges that need to be overcome before FePt or FePtX (where X represents a third material, e.g. carbon (C), titanium oxide (TiO2), or others) based composite films can be used for HAMR media applications. One of the challenges is to enable a fast cooling of the recording medium during the writing process. One approach may be to include a heat sink layer, but the introduction of the heat sink layer will cause some issues. These include (i) texture control where an epitaxial growth relationship is required between the heat sink layer and the MgO layer or an amorphous seedlayer is required for MgO growth, (ii) and surface roughness.
The fast cooling rate depends on the thickness and material of the heat sink layer in the medium, the physical distance between the recording layer and the heat sink layer, the layer structure of the HAMR medium, etc. There have been several proposals, such as to insert a heat sink layer into the HAMR medium layout by either using a crystallized heat sink layer material which has an epitaxial growth relationship with the magnesium oxide (MgO) intermediate layer in the medium, or insert an amorphous seedlayer between the heat sink layer and the MgO intermediate layer to enable the texture development of the MgO intermediate layer, thus enabling the texture control of the FePtX based HAMR medium.
A silver (Ag) based alloy could be one of the candidates for the heat sink layer owing to its epitaxial growth relationship with that of a (200) textured MgO. However, the growth of the Ag based alloy favors island growth, which results in an undesirably rough surface that will adversely affect flyability control of the recording medium. Furthermore, a Ag based heat sink layer will also imply a higher fabrication cost.
Copper (Cu)-based material has the advantages of better thermal conductivity, and a smoother surface. However, Cu does not have an epitaxial growth relationship with the MgO intermediate layer (e.g. the respective textures of Cu and MgO are not matched), and that means that an additional amorphous seedlayer needs to be deposited on top of the Cu based material or layer to enable the texture development of the MgO intermediate layer. The inserted additional layer will undesirably increase the physical distance between the Cu-based layer and the FePtX-based recording layer. Furthermore, the interfacial thermal conductance resulting from the additional layer, as the boundary thermal resistance dominates, could dramatically adversely affect the thermal spot size and the cooling rate of the media during the writing process, resulting in a larger thermal spot size and poor medium cooling efficiency. Therefore, a Cu or Cu based heat sink layer has not been perceived as desirable or even technically feasible.